Absorbing carbon dioxide from gas streams using an aqueous absorption solution

Abstract

Embodiments are directed to carbon dioxide absorbing apparatuses and methods thereof. An example apparatuses comprises an absorber column including an aqueous absorption solution and configured to contact an input gas stream containing carbon dioxide (CO2) with the aqueous absorption solution which absorbs CO2 from the input gas stream to generate a CO2-rich solution stream, the aqueous absorption solution including ammonia (NH3), methyl diethanol amine (MDEA), and potassium carbonate; and a regenerator column configured to receive the CO2-rich solution stream and output a CO2-lean solution stream and a CO2 gas stream.

Description

ABSORBING CARBON DIOXIDE FROM GAS STREAMS USING AN AQUEOUS ABSORPTION SOLUTIONGOVERNMENT RIGHTS

[0001] This invention was made with Government support under contract no. DE- FE0031597 awarded by the Department of Energy. The Government has certain rights in this invention.BACKGROUND

[0002] Carbon dioxide (CO2) is produced from many different gas stream sources, such as flue gas from a power plant. Capturing CO2 from gas streams leads to cleaner emissions and can help avoid penalties from Government agencies, and / or to meet targets from different Government agencies, environmental groups, and other sources. CO2 capture is not widely practiced due to high energy cost associated with existing capture processes. Historically, CO2 capture processes have required a significant amount of energy, which reduces the net power output of the source of the gas stream. For example, the output of a 500 megawatts (MW) (net) coal-fired power plant can be reduced to about 400 MW (net) after CO2 capture — a 20 percent energy penalty. To achieve commercial viability, this energy penalty needs to be reduced substantially.Therefore, there is a need for new and improved methods for CO2 capture for generating electricity efficiently while minimizing energy costs.

[0003] Ammonia-based CO2 capture has been considered as a promising alternative to costly conventional amine process. There are several ammonia-based technologies currently under development. Some major challenges of these processes are: (i) high energy intensive chilling requirement for flue gas cooling for absorber operation at temperatures less than 10 degrees Celsius, and (ii) large water usage and energy intensive sour stripping for ammonia emission reduction.SUMMARY

[0004] The present invention is directed to overcoming the above-mentioned challenges and others related to absorbing carbon dioxide (CO2) from a gas stream containing CO2.

[0005] Various aspects of the present disclosure are directed to an apparatus comprising an absorber column including an aqueous absorption solution and configured to contactan input gas stream containing CO2 with the aqueous absorption solution which absorbs CO2 from the input gas stream to generate a CCh-rich solution stream, the aqueous absorption solution including ammonia (NH3), methyl diethanol amine (MDEA), and potassium carbonate. The apparatus further includes a regenerator column configured to receive the CCh-rich solution stream and output a CCh-lean solution stream and a CO2 gas stream.

[0006] In some aspects, the regenerator column is configured to regenerate the aqueous absorption solution as the CCh-lean solution stream at a temperature of between about 100 degrees Celsius (C) and about 175 degrees C, or about 120 degrees C.

[0007] In some aspects, the regenerator column is configured to generate the CCh-lean solution stream and the CO2 gas stream from the CCh-rich solution stream at a pressure of between about 5 bar and about 20 bar and with a temperature gradient of about 30 degrees C to about 175 degrees C.

[0008] In some aspects, the aqueous absorption solution captures between 90 percent and 100 percent of the CO2 from the input gas stream and generates a CCh-depleted gas stream.

[0009] In some aspects, the apparatus further includes a heat exchanger coupled to the absorber column and configured to transfer heat between the heat exchanger and the input gas stream such that the input gas stream is at a temperature between about 18 degrees C to about 45 degrees C while input or prior to being input to the absorber column.

[0010] In some aspects, the apparatus further includes a second absorber column including the aqueous absorption solution and configured to contact a remaining portion of the input gas stream containing CO2 with the aqueous absorption solution and to generate a second CCh-rich solution stream. In such aspects, the regenerator column is further configured to receive the second CCh-rich solution stream and output a second CCh-lean solution stream.

[0011] In some aspects, the apparatus further includes pumps and valves configured to provide the CCh-lean solution stream to the absorber column and the second CCh-lean solution stream to the second absorber column, the CCh-lean solution stream having a higher ratio of Nfh / potassium carbonate than the second CCh-lean solution stream.

[0012] In some aspects, the absorber column includes first and second absorber regions with the aqueous absorption solution. In such aspects, the first absorber region is configured to contact the input gas stream containing CO2 with the aqueous absorptionsolution, generate the CCh-rich solution stream, and provide a remaining portion of the gas stream containing CO2 to the second absorber region. In such aspects, the second absorber region is configured to contact the remaining portion of the input gas stream containing CO2 with the aqueous absorption solution and generate a second CCh-rich solution stream from the remaining portion of the input gas stream containing CO2. And, in such aspects, the regenerator is configured to receive the CCh-rich solution stream and the second CCh-rich solution stream and to output the C Ch-lean solution stream, a second CCh-lean solution stream, and the CO2 gas stream.

[0013] In some aspects, the apparatus further includes a water wash coupled to the regenerator column and configured to capture NH3 from the CO2 gas stream exiting from the regenerator column.

[0014] In some aspects, the apparatus further includes a water wash coupled to the absorber column and configured to capture NH3 from the input gas stream with CO2 removed.

[0015] In some aspects, the MDEA includes activated-MDEA (a-MDEA).

[0016] Various aspects are directed to an apparatus comprising a first absorber section and a second absorber section in an absorber column, each of the first and second absorber sections including an aqueous absorption solution containing NEE, methyl MDEA, and potassium carbonate; and a regenerator column configured to receive the first and second CCh-rich solution streams and output a first CCh-lean solution stream to the first absorber section, a second CCh-lean solution stream to the second absorber section, and a CO2 gas stream. In such aspects, the first absorber section is configured to contact an input gas stream containing CO2 with the aqueous absorption solution which absorbs CO2 from the input gas stream to generate a first CCh-rich solution stream. In such aspects, the second absorber section is configured to contact a remaining portion of the input gas stream containing CO2, as received from the first absorber section, with the aqueous absorption solution which absorbs CO2 from the remaining portion of the input gas stream to generate a second CCh-rich solution stream and a CCh-depleted gas stream.

[0017] In some aspects, the aqueous absorption solutions are in packed sections of the first and second absorber sections which operate at between about 18 degrees C and about 45 degrees C.

[0018] In some aspects, the regenerator column is configured to generate the CO2 gas stream from the first and second CCh-rich solution streams at a pressure of betweenabout 5 bar and about 20 bar and with a temperature gradient of about 30 degrees C to about 175 degrees C.

[0019] In some aspects, the absorber column includes a first absorber column containing the first absorber section and a second absorber column containing the second absorber section.

[0020] In some aspects, the first absorber section is positioned vertically adjacent to the second absorber section in the absorber column.

[0021] Various aspects of the present disclosure are directed to a method comprising: contacting, in an absorber column, an input gas stream containing CO2 with an aqueous absorption solution including NH3, MDEA, and potassium carbonate to generate a CO2- rich solution stream and a CCh-depleted gas stream; and generating, using a regenerator column, a CCh-lean solution stream and a CO2 gas stream from the CCh-rich solution stream.

[0022] In some aspects, the method further includes receiving, in a second absorber section of the absorber column or in a second absorber column with the aqueous absorption solution, a remaining portion of the input gas stream containing CO2 from the absorber column or a first absorber section of the absorber column; contacting the remaining portion of the input gas stream containing CO2 with the aqueous absorption solution to absorb CO2 and to generate a second CCh-rich solution stream; and generating, using the regenerator column, a second CCh-lean solution stream.

[0023] In some aspects, the method further includes pumping: the CCh-lean solution stream to the first absorber section of the absorber column or to the absorber column; the second CCh-lean solution stream to the second absorber section of the absorber column or to a second absorber column, wherein the second CCh-lean solution stream has a lower ratio of Nfh / potassium carbonate than the (first) CCh-lean solution stream; and the CO2 depleted gas stream through a water wash to remove residual NH3 vapor.

[0024] In some aspects, the aqueous absorption solution includes: about 0.1 mole (mol) to about 4 mol MDEA; about 0.1 mol to about 4 mol potassium carbonate; and about 1 mol to about 7 mol NH3.

[0025] In some aspects, the method includes contacting the input gas stream with the aqueous absorption solution while at a temperature between about 18 degrees C and about 45 degrees C, and generating the CCh-lean solution stream and the CO2 gas stream while at a pressure between about 5 bar and about 20 bar and while at a temperature between about 30 degrees C and about 175 degrees C.

[0026] In some aspects, the method includes removing NH3 from the CCh-depleted gas stream using a water wash.BRIEF DESCRIPTION OF THE DRAWINGSVarious example embodiments can be more completely understood in consideration of the following detailed description in connection with the accompanying drawings, in which:

[0027] FIGs. 1A-1C illustrate example apparatuses for absorbing carbon dioxide (CO2) from a gas stream using an aqueous absorption solution, in accordance with the present disclosure.

[0028] FIG. 2 illustrates an example method of absorbing CO2 from a gas stream using an aqueous absorption solution, in accordance with the present disclosure.

[0029] FIGs. 3 A-3B illustrate diffusion coefficients of species and the ammonia (NH3) cycle at the gas-liquid boundary, in accordance with the present disclosure.

[0030] FIGs. 4A-4B show the CO2 absorption rate and NH3 vapor pressure at absorber 2 under different conditions, in accordance with the present disclosure.

[0031] FIG. 5 is a graph showing the gas transfer coefficient data obtained from a bench scale test of 30 weight percent (wt%) of an advanced mixed-salt process (A-MSP) solution indicating the effect of temperature on rate, in accordance with the present disclosure.

[0032] FIG. 6 is a graph showing representative integrated test results, in accordance with the present disclosure.

[0033] FIG. 7 is a graph showing a comparison of CO2 compositions in vapor phase for a CO2 mixed salt solution with methyl di ethanol amine (MDEA) added (51 wt% salt composition), in accordance with the present disclosure.

[0034] FIG. 8 is a graph showing CO2 loading verses CO2 pressure at 100 degrees Celsius (C) for a 10 molal mixed salt and 10 molal MDEA-mixed salts, in accordance with the present disclosure.

[0035] FIG. 9 is a graph showing power plant energy loss due to steam extraction, indicating that lower regeneration temperature and lower reboiler duty significantly improved net power output of the carbon capture integrated plant, in accordance with the present disclosure.

[0036] FIG. 10 is a graph showing efficiency as a function of CO2 loading for experiments at 20 degrees C, in accordance with the present disclosure.

[0037] FIGs. 11 A-l ID are graphs showing different groups of compositions and efficiency as a function of CO2 loading, in accordance with the present disclosure.

[0038] FIGs. 12A-12B are graphs showing the effect of temperature on efficiency and absorption rate at varying the CO2 loading for Composition 522, in accordance with the present disclosure.

[0039] FIGs. 13A-13B show modeling and laboratory measurements of CO2 partial pressure variations with CO2 loading for the Composition 522 at two temperatures, in accordance with the present disclosure.

[0040] FIG. 14 is a graph showing the desorption curves using a static autoclave setup, in accordance with the present disclosure.

[0041] FIG. 15 shows a schematic of an absorber block including two absorber columns with a water wash column added to the front end of the absorber columns for saturating incoming gas with water, in accordance with the present disclosure.

[0042] FIG. 16 shows a schematic of a regenerator column, in accordance with the present disclosure.

[0043] FIG. 17 is a graph showing the stability of the temperature of lean liquid 1 and lean liquid 2 drawn from the bottom and top regenerator stages during a six hour long run, in accordance with the present disclosure.

[0044] FIG. 18 is a graph showing regenerator pressure and CO2 flow rate during a six hour long run, in accordance with the present disclosure.

[0045] FIGs. 19A-19B show flowsheet models for A-MSP apparatuses, in accordance with the present disclosure.

[0046] FIG. 20 is a graph of corrosion rates of 304SS and 316SS when immersed in loaded and unloaded MEA solutions at 25, 40, and 80 degrees C, in accordance with the present disclosure.DETAILED DESCRIPTION

[0047] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure can be practiced. It is to be understood that other examples can be utilized, and various changes may be made without departing from the scope of the disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the disclosure is defined by the appended claims. Itis to be understood that features of the various examples described herein may be combined, in part or whole, with each other, unless specifically noted otherwise.

[0048] Carbon dioxide (CO2) is produced via a variety of processes and output in a gas stream, such as via flue gas stream from a fossil fuel power plant. As noted above, CO2 capture is not widely practiced due to high energy costs associated with existing capture processes. Embodiments of the present disclosure are directed to apparatuses and methods for capturing CO2 from a gas stream using an absorber column in which an input gas stream containing CCh is contacted with an aqueous absorption solution comprising both inorganic and organic species to remove CO2 therefrom, and a regenerator column in which the CO2 is regenerated from the solution at high pressure (e.g., greater than 5 bar). The CO2 loading to the aqueous absorption solution can be increased with a specific combination of mixed-salt and amine while reducing the parasitic energy consumption. The CO2 stripping temperature at the regenerator column can be reduced as compared to a mixed-salt only solution. Embodiments are directed to a Mixed Salt Process (MSP) that provides accelerated capture of CO2 from a gas stream using a mixed salt composition including an amine operating at ambient conditions.

[0049] The apparatus and / or method involves a technology that is an alternative to monoethanolamine (MEA) process. Such alternatives face major challenges, including high chemical cost, high solvent viscosity, low CCh-loading capacity, and low-pressure CO2 product. MSP can overcome many challenges inherent with amine-based or biphasic solvent system. The results from bench-scale MSP testing show that a two- component MSP, as an example, has an advantage over other solvent-based systems. An example of an MSP for accelerated captured of CO2 is described by US Patent No. 9,339,757, issued on May 17, 2016, and titled “Rate Enhancement of CO2 Absorption in Aqueous Potassium Carbonate Solutions By An Ammonia-Based Catalyst”, which is incorporated herein by reference in its entirety for its teachings. Embodiments in accordance with the present disclosure include an MSP composition with the addition of an amine. As further described, the apparatus and / or methods can capture CO2 at a high load with reduced number of gas-liquid exchanges, regenerate the CO2 at lower temperature and / or higher pressure than prior MSP, accelerate the capture into the solvent and achieve around 97 percent (%) or more CO2 capture, and / or reduce corrosion of vessels and columns compared to other amine-based apparatuses and methods.

[0050] In various embodiments, the aqueous absorption solution composition (sometimes herein interchangeably referred to as “an MSP solution” or “A-MSP solution”) and method of use can reduce the CO2 capture costs, which can allow for the CO2 capture technology to be widely accepted and implemented. With increasing environmental concerns, such as global warming and air quality, capturing CO2 can be important for different industries, such as fossil-fuel and other energy-based industries, to comply with emissions regulations.

[0051] In MSP chemistry, ammonia (NH3) plays a dual role of a catalyst and absorbent, due to the high mobility of reactivity of NH3 with CO2. NH3 absorbs large amounts of CO2 at low temperature and related CO2 at high temperature and pressure, making it a useful chemical in CO2 absorption compositions. By blending NH3 with other low- capacity and low-reactivity components, NH3 vapor pressure in the absorber can be suppressed and CO2 pressure in the regenerator column can be increased. Accordingly, the apparatuses and methods disclosed herein can be referred to as advanced MSP (A- MSP) in which the composition allows for a significant reduction in CO2 capture cost. In some embodiments, such as illustrated by FIGs. 1B-1C, the apparatus and / or method can include two isothermal absorbers and a selective regenerator and / or use thereof.

[0052] In MSP, CO2 is captured by chemical absorption that involves a series of ionic chemical reactions among CO2, NH3, K2CO3, and H2O. The MSP chemistry can include a gas / liquid-phase mass transfer followed by chemical reactions in the liquid phase. Selected reactions associated with MSP and the speciation of K2CO3- NH3-H2O-CO2 system include:CO2(gas (g)) < — > CO2(aqueous (aq)) Equation 1NH3(aq) + CO2(aq) + H2O (liquid(liq)) < — > (NH4)HCO3(aq) Equation 2(NH4)2CO3 + CO2(aq) + H2O (liq) 2(NH4)HCO3(aq) Equation 32NH3(aq) + CO2(aq) (NH4)NH2CO2Equation 4(NH4)NH2CO2(aq) + CO2(aq) + 2H2O (liq) 2(NH4)NCO3(aq) Equation 5K2COs(aq) + CO2(aq) + H2O (liq) + Catalyst < — > 2KHCO3(aq) +Catalyst Equation 6

[0053] In the advanced-MSP (A-MSP), the tertiary amine of methyl diethanol amine (MDEA) is added to the MSP solution. In such embodiments, K2CO3-NH3-MDEA- H2O-CO2 system has an additional reaction of Equation 7, in which MDEA is represented as R1R2R3N, where R1=R2= CH2CH2OH and R3 = CH3:RlR2R3N(aq) + CO2(aq) + H2O (liq) + Catalyst (RlR2R3NH)HCO3(aq) +Catalyst Equation 7

[0054] In the A-MSP, operational conditions, including temperature and CO2 loading, can be selected to avoid formation of solid species. The catalyst in the equations above can be the activated [(NEL -CCh)] species in both Equations 6 and 7. The chemical reactions in the NFE-based processes can all be reversible, with the direction of the reaction depending on pressure, temperature, and species concentration in the apparatus. At low temperatures, Equations 1-7 are exothermic reactions and proceed in the left-to- right direction of the equation and can require removal of heat from the process to maintain the absorption and desired absorption temperature. At high temperatures, Equations 1-7 are endothermic reactions and proceed in the right-to-left direction of the equation and can require energy to release gaseous CO2. The heat of the reaction can be tuned depending on the composition of the salt mixture of NH3 to MDEA+K (e.g., the ratio of NH3 to MDEA+K). The A-MSP, in accordance with embodiments, allows for low temperature of the absorption reaction, with high-loading of CO2, and low temperature / high-pressure regeneration, such as to obtain around 99% or more of pure dry CO2, and reducing emissions and water use over other ammonia and amine-based technologies.

[0055] Turning now to the figures, FIGs. 1 A-1C illustrate example apparatuses for absorbing CO2 from a gas stream using an aqueous absorption solution, in accordance with the present disclosure. The various apparatuses 100, 101, 103 use an aqueous absorption solution that includes NH3, MDEA, and potassium carbonate to capture CO2 from an input gas stream. In some embodiments, the MDEA can include an activated- MDEA (a-MDEA). The input gas stream can include any gas stream containing CO2 and which can be input from a variety of sources, such as flue gas from a fossil fuel power plant. Other example flue gas sources include natural gas power plants, plants associated with the cement industry, and other plants that output CO2-containing gas streams.

[0056] As shown by FIG. 1 A, in some embodiments, an example apparatus 100 includes an absorber column 102 including the aqueous absorption solution 104 and which is configured to contact an input gas stream containing CO2 105 (herein generally referred to as “the input gas stream 105”) with the aqueous absorption solution 104 to generate a CCh-rich (e.g., CO2 loaded) solution stream 109. As noted above, theaqueous absorption solution 104 includes NH3 106, MDEA 108, and potassium carbonate 110.

[0057] As used herein, a CCh-rich solution stream includes and / or refers to a solution in a liquid phase containing at least a portion of the CO2 from the input gas stream 105 loaded to the aqueous absorption solution 104, which is output by the absorber column 102. As further described below, a CCh-lean solution stream includes and / or refers to a solution in a liquid phase which contains (significantly) less CO2 than the CCh-rich solution stream. For example, a CCh-lean solution stream 113 can include the CCh-rich solution stream 109 with the loaded CO2 removed, and which is output by the regenerator column 112.

[0058] As used herein, an absorber column includes and / or refers to a column and other components that moves material from a gas phase to a liquid phase, and can be used to wash gases and / or remove pollutants. In some embodiments, the absorber column 102 can be a state-to-state flow system that absorbs impurities from the gas phase into the liquid phase. In many cases, the absorber column 102 can be a packed tower in which gas flows up and liquid flows down. For example, an absorber column can be a vertically-oriented column (e.g., a height being greater than a circumference), which can be divided into sections. Each section or at least a portion thereof can be packed sections which may have a stage. Thus, an absorber column can contain a single section or a plurality of sections therein. The absorber column 102 can be a single-stage absorber column (e.g., only a single physical column) with a plurality of sections within the single stage, or can be a multi-stage absorber column (e.g., a plurality of separate columns), wherein each stage is a single section, as further described herein.

[0059] In some embodiments, the aqueous absorption solution 104 (or solutions) captures between 90% and 100% of the CO2 from the input gas stream 105 and generates a CCh-depleted gas stream 107. In some embodiments, as further described herein, the CCh-depleted gas stream 107 is output from a second absorber and / or after passing through a water wash 114-1 to remove NH3. For example, the CCh-depleted gas stream 107 output from the absorber column 102 can be a purified gas stream (e.g., purified flue gas stream).

[0060] The aqueous absorption solution 104 can be in a packed section of the absorber column 102. In some embodiments, the absorber column 102 can include additional packed sections. For example, the absorber column 102 can include an additionalpacked section of stainless steel packing or other material of packing, which is illustrated in some figures with an X.

[0061] In some embodiments, and as illustrated by and referring to FIG. 1C, the absorber column 102 includes first and second absorber sections 120-1, 120-2, each including aqueous absorption solution 104-1, 104-2 (e.g., in packed sections). The first absorber section 120-1 is configured to contact the input gas stream 105 with the aqueous absorption solution 104-1, generate the CCh-rich solution stream 109-1, and provide a remaining portion of the input gas stream 115 to the second absorber section 120-2. The second absorber section 120-2 is configured to contact the remaining portion of the input gas stream 115 with the aqueous absorption solution 104-2 and generate a second CCh-rich solution stream 109-2 from the remaining portion of the input gas stream 115. As further described below, the regenerator column 112 is configured to receive the CCh-rich solution stream 109-1 and the second CCh-rich solution stream 109-2 and to output the CCh-lean solution stream 113-1, a second CCh-lean solution stream 113-2, and the CO2 gas stream 111.

[0062] As noted above, in some embodiments, the absorber column 102 includes two sections. In some embodiments, the first section is the “bottom section” of the absorber column 102, and the second section is the “top section” of the absorber column 102.

[0063] In some embodiments of the single-stage absorber column 102, the various sections (e.g., first and second sections) are separated by a physical barrier such as a screen, baffles, or the like. In some such embodiments, such barrier is a barrier against liquids but is permeable to gases. In some embodiments, the first section is the “bottom section” and extends from the bottom of the absorber column 102 (e.g., the lowest-most point in the column) to the barrier between the first and second section. The second section is the “top section” and extends from the top (e.g., highest point) of the absorber column 102 to the barrier between the second and first section. An optional third section, when present, is the “middle section” and exists between the two barriers. When the middle section is absent, the first and second sections can be equal in size (e.g., each 50% of the total column height), or can be unequal in size (e.g., the first section is 20, 30, 40, 60, 70, or 80% of the total column height). When the middle section is present, the three sections can be equal in size (e.g., each 33% of the total column height) or cab be unequal in size, in which case any suitable proportions of the three sections (e.g., 10 / 80 / 10, 30 / 40 / 30, 50 / 30 / 20) can be used.

[0064] In some embodiments of the single-stage absorber column, no physical barriers are present, and the various sections are identifiable in part by physical location and in part with reference to the contents of the aqueous absorption solution. For example, in a two-section column (e.g., the optional third section is not present), the first section is the “bottom section” and extends from the bottom-most point of the absorber column. The second section is the “top section” and extends from the top-most point of the absorber column 102. The two sections encompass the entire height of the absorber column 102. The sections meet, and the meeting point / area can be at the mid-point of the absorber column 102 (halfway between the extremities) or can be at least 10, 20, 30, 40, or 50% of the distance between the mid-point and either extremity. For example, the first section can include the bottom 30, 40, 50, 60, 70, or 80% of the total column height. Similarly, the second section can include the top 20, 30, 40, 50, 60, or 70% of the total column height. In a three-section column (e.g., the optional third section is present), the third (e.g., middle) section can encompass the midpoint of the column, and can include between 15-40 or 20-35% of the total column height, with the first and second sections forming the remaining portions. It is not, however, necessary for the middle section to encompass the midpoint — the middle section is merely between the first and second sections. In some embodiments, the sections are all of the same size (e.g., in a two- section column, both sections are 50% of the height and in a three-section column, all three sections are 33%). In embodiments, the sections can be identified and recognized by the composition of the aqueous absorption solution 104 therein.

[0065] In some embodiments of the multi-stage absorber column, the absorber column 102 includes a plurality of separate, individual absorber columns with linkages (e.g., input / output ports, conduits) between the stages. The linkages provide fluid (e.g., liquid, gas, or both) communication between successive stages. In such embodiments, the absorber column 102 can include two or three (or more) stages each containing an aqueous absorption solution and connected via a linkage to one or more adjacent stage(s). For example, a first stage is the “bottom section” of the absorber column 102, a second stage is the “top section”, and an optional third stage is the “middle section” of the absorber column 102.

[0066] In some embodiments, a physical barrier between sections is present, and liquid is collected to a tray at the bottom of the top absorber column section. The liquid collected in the tray can overflow down to the bottom absorber column section. A portion of the liquid collected on the tray can be fed back to the top of the absorbercolumn 102 and / or get mixed with liquid in the top section of the absorber column 102. This combined flow is then pumped to the regenerator column 112.

[0067] In some embodiments, and as illustrated by FIG. IB, the apparatus 100 further includes a second absorber column. For example and referring to FIG. IB, the second absorber column 102-2 can include the aqueous absorption solution 104-2 and is configured to contact a remaining portion of the input gas stream 115 with the aqueous absorption solution 104-2 and to generate a second CCh-rich solution stream 109-2. As further described below, the regenerator column 112 can receive the second CCh-rich solution stream 109-2 and output a second CCh-lean solution stream 113-2. In such embodiments, the first and / or second absorber column 102-1, 102-2 can include a section or multiple sections, such as having an additional packed section including stainless steel packing or other packing material.

[0068] In some embodiments, as noted above, multiple sections of the absorber column 102 or multiple absorber columns contain the aqueous absorption solution 104, and the composition of the aqueous absorption solution 104 can vary between. The composition of the aqueous absorption solution 104 in any section or column can be dependent upon a variety of factors such as the material input to the section and the conditions (e.g., temperature, etc.) within the section and / or column. The material inputs to the various sections is determined by the interconnectivity arrangement of the apparatus, as described herein. Generally, the aqueous absorption solution 104 includes water, MDEA 108, dissolved NH3 106, and potassium carbonate 110. Due to various factors including reactions between MDEA 108, NH3 106, and potassium carbonatel lO dissociation, and the like, other species can be present in the NH3. Such other species include ammonium salts such as ammonium carbonate and ammonium bicarbonate.

[0069] Referring back to FIG. 1 A, the apparatus 100 further includes a regenerator column 112 configured to receive the CCh-rich solution stream 109 and output a CO2- lean solution stream 113 and a CO2 gas stream 111. The CCh-lean solution stream 113 can include the aqueous absorption solution 104 or a modified form thereof, and is in a liquid phase. The CO2 gas stream 111 can include CO2 in a gas phase, and with aqueous absorption solution 104 (e.g., ammonia and other components) removed therefrom. A regenerator column, as used herein, includes and / or refers to a device that transfers heat energy from a thermal storage medium, such as steam, to a fluid, such as to the CCh-rich solution stream(s) 109, and which can cause regeneration of the aqueous absorption solution 104 as the CCh-lean solution stream 113. More particularly, the regeneratorcolumn 112 can desorb CCh from the CCh-rich solution stream(s) 109 and regenerate the aqueous absorption solution 104 as the CCh-lean solution stream 113. In some embodiments, multiple CCh-lean solution streams 113 are generated which have varying NH3 to K ratios, and which are reused as the aqueous absorption solution(s) 104 in the absorber column(s) 102.

[0070] In some embodiments, the regenerator column 112 is a vertically-oriented column (e.g., with a height greater than a circumference). As noted above, the regeneration column 112 can include sections therein, wherein a “section” is within the regenerator column 112 with a distinct function or containing a solution with a distinct composition.

[0071] The regenerator column 112 can include a column including a plurality of stages and is coupled to or otherwise includes a reboiler 117 or other type of heat exchanger. The regenerator column 112 can further include a stripping column 119. As used herein, a reboiler includes and / or refers to a heat exchanger that generates vapor which is fed to a column, such as distillation column or stripping column. A stripping column includes and / or refers to a chemical device configured to remove organic substances or volatiles from a liquid stream using a vapor stream. The CCh-rich solution stream 109 (or streams 109-1, 109-2 in FIGs. 1B-1C) are passed and input to an upper stage of the regenerator column 112 and the reboiler 117 generates vapor stream, which is passed through the stripping column 119 in a lower middle stage of the regenerator column 112 to increase a temperature to between about 100 degrees Celsius (C) and about 175 degrees C and to desorb (e.g., strip) CO2 from the CCh-rich solution stream 109. The CCh-lean solution stream 113 is then drawn from the bottom stage of the regenerator column 112 to the absorber column 102 and the CO2 gas stream I l l is drawn through the column of the regenerator column 112 and output (e.g., after polishing by the water wash 114-2).

[0072] As such, the regenerator column 112 and absorber column 102 are in fluid communication to pass the CCh-rich solution stream 109 and the CCh-lean solution stream 113. Each of the absorber column 102 and the regenerator column 112 are configured to receive the respective streams via suitable input / output ports and conduits that transfer the streams from source to destination. As further described below, additional components, such as pumps, valves, filters, and others can be present. For example, in some embodiments, the apparatus 101 can include a conduit providing fluid communication between a section of the regenerator column 112 containing a CCh-lean solution stream 113 and the respective absorber column 102.

[0073] As a specific example, the CCh-rich solution stream 109 can be extracted from the absorber column 102 (e.g., from the bottom section of the absorber column 102) and is pumped to the regenerator column 112. The CCh-rich solution stream 109 enters the regenerator column 112 at or near the top of the column 112. Once inside the regenerator column 112, the CO2-rich solution stream 109 is subjected to conditions suitable for desorption of CO2 and formation of a (purified) CO2 gas stream 111 (e.g., high purity CO2 gas). Thus, outputs of the regenerator column 112 include a purified CO2 gas stream 111 and a CO2-depleted solution, e.g., the CO2-lean solution stream 113. The purified CO2 gas stream 111 can be extracted from any suitable location within the regenerator column 112, such as the top or near the top section of the column (e.g., within 1, 2, 3, 4, or 5% of the uppermost point of the column). The CCh-lean solution stream 113 can be pumped to the absorber column 102. For example, in embodiments including a single absorber column 102 with multiple absorber sections (e.g., 120-1, 120-2), the NH3 rich stream (e.g., CCh-lean solution stream 113-1) can be pumped to the mid-section of the absorber column 102 (e.g., the vertical midpoint or within 5, 10, 15, 20, or 25% of the vertical midpoint of the absorber column 102), and the NH3 deficient stream (e.g., CCh-lean solution stream 113-2) is pumped to the bottom of the absorber column 102 (e.g., the lowest point or within 5, 10, or 15% of the lowest point of the absorber column 102).

[0074] In various embodiments, the regenerator column 112 can regenerate the aqueous absorption solution 104 as the CCh-lean solution stream 113 (via operating) at a temperature of between about 100 degrees C and about 175 degrees C. In some embodiments, the CCh-lean solution stream 113 can be regenerated at between about 125 degrees C and about 175 degrees C, about 150 degrees C and about 175 degrees C, about 100 degrees C and about 150 degrees C, about 100 degrees C and about 125 degrees C, about 120 degrees C and about 125 degrees C, or about 120 degrees C, among other values and ranges.

[0075] In some embodiments, the regenerator column 112 is configured to generate the CCh-lean solution stream 113 and the CO2 gas stream 111 from the CCh-rich solution stream 109 (via operating) at a pressure of between about 5 bar and about 20 bar and with a temperature gradient of about 30 degrees C to about 175 degrees C. In some embodiments, the pressure can be between about 5 bar and about 15 bar, about 5 bar and about 10 bar, about 5 bar and about 7 bar, about 10 bar and about 20 bar, about 15 bar and about 20 bar, about 5 bar, about 10 bar, about 15 bar, or about 20 bar, among othervalues. In some embodiments, the temperature gradient can between about 30 degrees C to about 150 degrees C, 30 degrees C to about 125 degrees C, 30 degrees C to about 120 degrees C, 50 degrees C to about 175 degrees C, 75 degrees C to about 175 degrees C, 40 degrees C to about 175 degrees C, 60 degrees C to about 175 degrees C, 40 degrees C to about 125 degrees C, 60 degrees C to about 125 degrees C, 40 degrees C to about 120 degrees C, or 60 degrees C to about 120 degrees C, among other temperature gradient ranges. For example, a first temperature at a first section (e.g., top section or near the top section) of the regenerator column 112 can be relatively low (e.g., 30 degrees C to 90 degrees C) as compared to a second temperature at a second section (e.g., bottom section or section near the bottom) of the regenerator column 112 (e.g., 100 degrees C to 175 degrees C). Accordingly, in some embodiments, a temperature gradient exists within the regenerator column 112 such that the temperature of the CO2- rich solution stream 109 at a first (e.g., top) section of the regenerator column 112 is lower than the temperature of the CCh-rich solution stream 109 at a second (e.g., bottom) section of the regenerator column 112.

[0076] In embodiments during operation, water, NH3, and CO2 evaporate from the bottom of the regenerator column 112, and this stream heats the down coming mixed salt stream leaving a potassium rich solution at the bottom of the regenerator column 112. In embodiments, the composition of potassium salts and MDEA in the bottom of the regeneration column 112 is between about 0.1 to about 4 molal, while the concentration of NH3 salts is between about 1 to about 6 molal.

[0077] In some embodiments, the apparatus 100 can further include heat exchangers 116-1, 116-2, 117. A heat exchanger includes and / or refers to a device that transfers heat between mediums without mixing them. The heat exchangers 116-1, 116-2, 117 can be located along solution stream flows (e.g., conduits that the streams are passed along) to provide heat energy. Example heat exchangers include cooling coils, heating coils, reboilers, heat sinks, scrubbers, and condensers, among others.

[0078] For example, a heat exchanger 116-1 can be coupled to the absorber column 102 and configured to transfer heat between the heat exchanger 116-1 and the input gas stream 105 such that the input gas stream 105 is at a temperature of between about 18 degrees C to about 45 degrees C while input or prior to being input to the absorber column 102. In some embodiments, the input gas stream 105 can be at a temperature of between 20 degrees C to about 45 degrees C, 25 degrees C to about 45 degrees C, 30 degrees C to about 45 degrees C, 40 degrees C to about 45 degrees C, 18 degrees C toabout 40 degrees C, 18 degrees C to about 35 degrees C, 18 degrees C to about 30 degrees C, 18 degrees C to about 25 degrees C, 18 degrees C to about 20 degrees C, 20 degrees C to about 40 degrees C, 20 degrees C to about 35 degrees C, 20 degrees C to about 30 degrees C, or 20 degrees C to about 25 degrees C, among other temperatures.

[0079] As another example, a heat exchanger 116-2 can be coupled to a conduit and configured to pass (e.g., push or pull) the CCh-lean solution stream 113 from the regenerator column 112 to the absorber column 102. The heat exchanger 116-2 can transfer heat between the heat exchanger 116-1 and the CCh-lean solution stream 113 such that the CCh-lean solution stream 113 input to the absorber column 102 is at the temperature of between about 18 degrees C and 45 degrees C or the any of the above listed temperatures ranges associated with heat exchanger 116-1.

[0080] The apparatus 100 can further include pumps and valves to pass the various gases and liquid solutions throughout the apparatus 100. For example, a pump 118 can flow the CCh-rich solution stream 109 from the absorber column 102 to the regenerator column 112. Similarly, although not illustrated, a pump can flow the CCh-lean solution stream 113 from the regenerator column 112 to the absorber column 102. The pump(s) can be located in or coupled to conduits of the apparatus 100 which connect the absorber column 102 and the regenerator column 112. In some embodiments, and referring to FIG. IB, pumps 118-1, 118-2, 118-3, 118-4 can provide the CCh-lean solution stream 113-1 to the absorber column 102-1 and the second CCh-lean solution stream 113-2 to the second absorber column 102-2, the CCh-lean solution stream 113-1 having a higher ratio of NFh / potassium carbonate than the second CCh-lean solution stream 113-2.

[0081] Referring back to FIG. 1 A, in some embodiments, the apparatus 100 can include water washes 114-1, 114-2 which can be coupled to an absorber column 102 and / or regenerator column 112 to capture residual NH3 from the streams or for other purposes. In some embodiments, the water washes can remove most (e.g., greater than 50, 60, 70, 80, 90, or 95%) of NH3 from the respective streams. As used herein, a water wash includes and / or refers to a device or components used to remove condensable constituents from a medium, such as from gas to be output from the apparatus 100. In some instances, a water wash can include bubble caps and a fluid chamber for liquid hold. As may be appreciated, the water washes 114-1, 114-2 can include input and output water streams, along with input and output ports for the water streams, as illustrated by the arrows pointing into and out of the water washes 114-1, 114-2. As an example, a first water wash 114-1 can be located in or otherwise coupled to the absorbercolumn 102 or otherwise proximate to the aqueous absorption solution 104 (such as to an absorber section). A CCh-depleted gas stream 107 which is output from the absorber column 102 and has CO2 removed can flow through the first water wash 114-1 to remove NH3 therefrom. As another example, a second water wash 114-2 can be located in or otherwise coupled to the regenerator column 112, with the second water wash 114- 2 being proximate to an upper stage of the regenerator column 112. As noted above, in some embodiments, a stripping column 119 can be proximate to a lower middle stage of the regenerator column 112. A CO2 gas stream 111 that is output from the regenerator column 112 can be formed via the stripping column 119 and reboiler 117 and then flown through the second water wash 114-2 to remove NH3 from the CO2 gas stream 111 which is exiting from the regenerator column 112, such as being passed from a particular stage of the regenerator column 112 associated with the stripping column 119 to the second water wash 114-2. For example, vapor stream from the reboiler 117 can be drawn through the stripping column 119 and used to increase the temperature of the CCh-rich solution stream 109 for regenerating the aqueous absorption solution 104 and CO2 gas 111, and the CO2 gas I l l is polished by the second water wash 114-2 and then output from the regenerator column 112. As sometimes used herein, “polishing” includes and / or refers to the removal of impurities from a stream, such as removing NH3.

[0082] Embodiments are not limited to arrangements illustrated by FIGs. 1 A-1C. As an example variation, in some embodiments, at least one of the water washes 114-1, 114-2 can be formed in a separate column (e.g., a water wash column) which is coupled to the absorber column 102 and / or regenerator column 112.

[0083] The apparatus 100 can include additional components, such as but not limited to valves, flow meters, temperature sensors, level sensors, filters, and / or a controller. For example, a controller can instruct components of the apparatus 100, such as the pumps, heat exchangers, and other components, to drive the process of capturing CO2 from the input gas stream 105. The controller can be used to adjust different parameters, including those further described herein, and which can be based on sensor signals from temperature and / or level sensors. For example, the temperature, pressure, and / or flow of the absorber column 102, regenerator column 112, and conduits therebetween can be monitored and regulated by the controller and associated sensors.

[0084] In operation, the apparatus 100 includes two output gas streams, the CCh- depleted gas stream 107 output by the absorber column 102 and the purified CC gas111 output by the regenerator column 112. In some embodiments, the CCh-depleted gas stream 107 can be output to the atmosphere and the CO2 gas 111 can be sequestered or utilized for other applications.

[0085] In various embodiments and as further illustrated by Table 5 below, the apparatus 100 and / or any apparatus described herein can have reduced corrosion during operation as compared to prior solutions and which can allow for at least portions (e.g., components) of the apparatuses to be formed of steel, such as low-cost steel.

[0086] FIG. IB illustrates an example apparatus comprising two absorber columns. As shown, the apparatus 101 includes two absorber columns 102-1, 102-2, a regenerator column 112, and optionally other auxiliary components as further described herein. The first absorber column 102-1 includes a first absorber section 120-1 including aqueous absorption solutionl04-l and the second column 102-2 includes a second absorber section 120-2 including aqueous absorption solution 104-2. As further described herein, the first absorber section 120-1 can operate with a higher ratio of NFh / potassium carbonate than the second absorber section 120-2. In some embodiments, the apparatus 101 of FIG. IB can include an implementation of and / or at least some of substantially the same features and attributes of the apparatus 100 of FIG. 1A. The common features and attributes are not repeated for ease of reference.

[0087] As shown by FIG. IB, each of the absorber sections 120-1, 120-2 can include aqueous absorption solutions 104-1, 104-2 containing NH3 106, MDEA 108, and potassium carbonate 110. As previously described, in some embodiments, the MDEA 108 can include a-MDEA. In some embodiments, the first absorber section 120-1 is configured to contact an input gas stream containing CO2 105 with the aqueous absorption solution 104-1 which absorbs CO2 from the input gas stream 105 to generate a first CCh-rich solution stream 109-1. The second absorber section 120-2 is configured to contact a remaining portion of the input gas stream containing CO2 115, as received from the first absorber section 120-1, with the aqueous absorption solution 104-2 which absorbs CO2 from the remaining portion of the input gas stream 115 to generate a second CCh-rich solution stream 109-2 and a CCh-depleted gas stream 107. The regenerator column 112 is configured to receive the first and second CCh-rich solution streams 109-1, 109-2 and output a first CCh-lean solution stream 113-1 to the first absorber section 120-1, a second CCh-lean solution stream 113-2 to the second absorber section 120-2, and a CO2 gas stream 111.

[0088] Accordingly, the first absorber section 120-1 is in fluid communication with the second absorber section 129-2 to pass the portions of the input gas stream 115 and the regenerator column 112 is in fluid communication with the first and second absorber sections 120-1, 120-2 to pass the CCh-rich solution streams 109-1, 109-2 and the CO2- lean solution streams 113-1, 113-2. Each of the absorber columns 102-1, 102-2 and the regenerator column 112 can be configured to receive the respective streams via suitable input / output ports and conduits that transfer the streams from source to destination.

[0089] As described in connection with the apparatus 100 of FIG. 1 A, the apparatus 101 can include various additional components, sometimes referred to as “auxiliary components”. Examples of additional components include pumps, valves, filters, and others. For example, the apparatus 101 can include heat exchanger(s) 116-1, 116-2, 116- 3, 116-4, 116-5, 116-6, 117 to adjust the temperature of the solutions and gases, and pumps 118-1, 118-2, 118-3, 118-4 to provide flow of gas and solution streams. Apparatuses can include additional or fewer heat exchanges, pumps, and other auxiliary components than illustrated by FIGs. 1 A-1C. The example auxiliary components (e.g., heat exchangers and pumps) can include at least some of substantially the same features and attributes as those previously described in connection with the apparatus 100 of FIG. 1A. For example, the absorber columns 102-1, 102-2 can include an additional section 121-1, 121-2, which include packed sections of steel.

[0090] In some embodiments, the apparatus 101 can include water washes 114-1, 114-2 5- which can be coupled to a respective absorber column 102-1, 102-2 and / or regenerator column 112 to capture NH3 from the streams. As previously described, the apparatus 101 can additionally include a stripping column 119 located within the regenerator column 112. For example, a first water wash 114-1 can be located in the second absorber column 102-2 or otherwise proximate to the second absorber section 120-2. The CCh-depleted gas stream 107 which is output from the second absorber section 120-2, and has CO2 removed, can flow through the first water wash 114-1 to remove NEE therefrom. As another example, a second water wash 114-2 can be located in the regenerator column 112 or otherwise proximate to an upper stage of the regenerator column 112. A CO2 gas stream 111 to be output from the regenerator column 112 can flow through the second water wash 114-2 to remove NEE in the CO2 gas stream 111. The stripping column 119, as previously described, can be used with the reboiler 117.

[0091] In some embodiments (including those illustrated by FIG. 1 A and 1C), the aqueous absorption solutions 104-1, 104-2 are in packed sections, e.g., the first and second absorber section 120-1, 120-1 are packed sections, and can operate at between about 18 degrees C and about 45 degrees C, or at ambient temperature. Further, the regenerator column 112 can be configured to generate the CO2 gas stream 111 from the first and second CCh-rich solution streams 109-1, 109-2 at a pressure of between about 5 bar and about 20 bar and with a temperature gradient of about 30 degrees C to about 175 degrees C, as previously described.

[0092] The following describes a specific example operation of the apparatus 101 of FIG. IB. The apparatus 101 can be integrated downstream of the system that generates a gas stream containing CO2 105. For example, the apparatus 101 can be downstream of a power plant flue gas outlet. Flue gas from the power plant can be cooled to between about 30 degrees C and about 40 degrees C by the heat exchanger 116-1 and then enters the first absorber section 120-1 having the aqueous absorption solution 104-1 which absorbs between about between 60% to about 80% of the CO2 from the input gas stream 105. The remaining portion of the input gas stream 115 is passed to the second absorber section 120-2 having the aqueous absorption solution 104-2 which absorbs the remaining or substantial amount of the remaining CO2 from the remaining portion of the input gas stream 115. The use of two absorbers can reduce the NH3 carryover, as further described herein. Both absorber sections 120-1, 120-2 can operate with liquid recycled using pumps to flow the solutions and heat exchangers (e.g., 116-2, 116-3, 116-4, 116-5, 116-6) to remove heat of the reaction and keep the solution(s) at the optimum temperature for efficient absorption and minimum NH3 slip. With this two-stage absorption, the second absorption section 120-2 can be operated with the highest CO2 loading in the range of 0.6-0.7 moles of CO2 per mole of NH3, potassium, and MDEA. Each absorber sections 120-1, 120-2 can output CCh-rich solution streams 109-1, 109-2.

[0093] The CCh-rich solution streams 109-1, 109-2 from the absorber sections 120-1, 120-2 are sent to regenerator column 112 which produces two CCh-lean solution streams 113-1, 113-2 and a CO2 gas stream 111 from the CCh-rich solution streams 109- 1, 109-2. The first CCh-rich solution stream 109-1 from the first absorber section 104-1 can contain higher amounts of CO2 than the second CCh-rich solution stream 109-2 due to the first absorber section 120-1 operating with a higher ratio of NH3 to potassium carbonate (e.g., MDEA plus potassium). The resulting CCh-lean solution streams 113-1, 113-2 generated by the regenerator column 112 can include a first CCh-lean solutionstream 113-1 provided to the first absorber section 120-1 and a second CCh-lean solution stream 113-2 provided to the second absorber section 120-2, where the first CCh-lean solution stream 113-1 has the higher ratio of NH3 to potassium carbonate as compared to the second CCh-lean solution stream 113-2. The first CCh-lean solution stream 113-1 can be referred to as “a high NH3 / (MDEA + K) mixed salt” and the second CCh-lean solution stream 113-2 can be referred to as “a low NHs / (MDEA + K) mixed salt”. The two CCh-lean solution streams 113-1, 113-2 can be drawn from the lower-middle stage and bottom stage of the regenerator column 112. The regenerator column 112 can be operated under high-pressure isobaric conditions, e.g., 5-20 bar, and have a temperature gradient in the column with the bottom having a higher temperature than the top stage (e.g., top at around 30 degrees C and bottom around 120 to 170 degrees C). At the bottom stage with the higher temperature, the NH3 in the regenerator column 112 can be vaporized along with CO2 to make the second CCh-lean solution stream 113-2, e.g., low NH3 / (MDEA + K) mixed salt, for use in the second absorber section 120-2. Vaporized NH3 gets reabsorbed as the vapor moves up the regenerator column 112 thereby creating the first CCh-lean solution stream 113-1, e.g., high NH3 / (MDEA + K) mixed salt, for use in the first absorber section 120-1. As previously described, the reboiler 117 generates a vapor stream which is passed through the stripping column 119 in a (lower) middle stage of the regenerator column 112 and increases the temperature to between about 100 degrees C and about 175 degrees C to regenerate the CO2 gas stream 111 and the CCh-lean solution streams 113-1, 113-2 from the CCh-rich solution streams 109-1, 109-2.

[0094] The apparatus 101, as well as apparatuses 100 and 103, can allow for operating the regenerator column 112 at a low temperature (e.g., around 100 degrees C) and high pressure (e.g., around 5-20 bar), thus substantially reducing water stripping and resulting in a dry or near-dry CO2 gas stream 111 (EEOvap / CCh less than 0.2) at high pressure. This can reduce regenerator column 112 size and CO2 compression energy costs (e.g., operating expenditure (OPEX) reduction) and remove the first CO2 compression stage (e.g., capital expenditure (CAPEX) reduction).

[0095] In such apparatuses (and methods of using), the absorber(s) have enhanced reaction rates compared to NH3 and / or carbonate processes. For example, the CO2 absorption rate in the first absorption section 120-1 is high due to the NFE / potassium (K) ratio and high pH. That is, the first absorber section 120-1 can be enriched in NH3, and thereby operate with a high NH3 / K ratio that can be greater than at least 1, such as1, 1.1, 1.2, 1.3, 1.4, 1.5, 2, 3, or 5. The relatively high concentration of NH3 provides enhanced CO2 capture rate and overall capture capacity. Accordingly, when using a single absorber column, as shown by FIG. 1C, the first absorber section 120-1 can the “bottom section” of the absorber column, and in operation, receives the input gas stream 105 to be treated (e.g., a flue gas from a power plant, etc.).

[0096] In the second absorption section 120-2, the rate enhancement is achieved by NH3 acting as a promoter to reduce the boundary layer associated with the gas-to-liquid mass transfer for gaseous CO2 absorption and the diffusion of aqueous CCh2' in the solution. The second absorption section 120-2 can be depleted in NH3, and have a low NH3 / K ratio of less than 1, such as 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, or 0.3. Accordingly, when using a single absorber column, as shown by FIG. 1C, the second absorption section 120-2 can be the “top section” which can include the water wash 114-1 and an outlet for the CO2- depleted gas stream 107. The reduced NH3 concentration in the second absorption section 120-2 can reduce the overall NH3 emissions from the absorber column 102.

[0097] Without being bound by theory, it is believed that undissociated NH3 present in the aqueous absorption solution 104-1, 104-2 has a high diffusion rate compared to other ionized and undissociated dissolved species, such as carbonate, bicarbonate, or dissolved carbon dioxide (see FIG. 3 A). Therefore, the NH3(g) reacts with CO2(g) at the gas / liquid interface forming a transient complex that is dissociated by several pathways: (i) NH3CO2* + NFE(g) -+ NH2CO2- + NH4+and (ii) NH3CO2* + H2O(liq) -+ NHCCh' + NH4+. In addition, the complex of NH3CO2* can dissociate back to NH3(aq) and CO2(aq) increasing in dissolved CCh(aq). This allows for rate enhancement of slow CO2 absorption reactions by in-situ inorganic moiety, NH3CO2* formation as further shown in FIG. 3B. This NHs-based inorganic moiety has a high diffusion coefficient that enhances the mass transport of the carbonate ion across the gas-liquid interface into the solution, increasing the activity of CO2 in the dissolved phase. The net result is NH3 acting as a promoter to shuttle the carbonate ion, which enhances rates of slower reactions and results in a high rate of CO2 absorption by the MSP composition. The same rate enhance action of NH3CO2* activator promotes the CO2 absorption rate of MDEA.

[0098] As noted above and further described below, in various embodiments, the first absorber section 120-1 has a high NH3 / (MDEA + K2CO3) ratio, and thus the CO2 capture is driven by the NEE. The second absorber section 120-2 is operated with lowNHs / (MDEA + K2CO3) ratio, and NH3 plays the role of an absorbent and a promoter, thus enhancing the slow absorptions reactions of MDEA and K2CO3.

[0099] Accordingly, in some embodiments, the first absorber section 120-1 can be operated with the high NH3 / K (e.g., 3-4) and the second absorber section 120-2 can be operated with low NH3 / K (less than 1) to maximize the absorption of CO2 from the input gas stream 105 and minimize NEE carried over to the water wash 114-1 with the scrubbed gas stream. For example, the first absorber section 120-1 can be operated with a NH3 / (MDEA + K2CO3) ratio above 1 and the second absorber section 120-2 can operated with a NH3 / (MDEA + K2CO3) ratio below 1. The cleaned CCh-depleted gas stream 107 from the water wash 114-1 can contain less than 10 parts per million (ppm) NH3, which can meet emission requirements.

[0100] FIG. 1C illustrates an example apparatus comprising an absorber column with two absorber sections. In various embodiments, the apparatus 103 of FIG. 1C can include an implementation of or include at least some of substantially the same features and attributes of the apparatus 101 of FIG. IB, but with the first and second absorber sections 120-1, 120-2 in the same column 102. The common features and attributes are not repeated for ease of reference. In such embodiments, the first absorber section 120-1 can be positioned vertically adjacent to the second absorber section 120-2 in the absorber column 102, as shown by FIG. 1C.

[0101] FIG. 2 illustrates an example method of absorbing CO2 from a gas stream using an aqueous absorption solution, in accordance with the present disclosure. In some embodiments, the method 230 can be implemented using any of the apparatuses 100, 101, 103 of FIGs. 1A-1C.

[0102] As shown at 232, the method 230 includes contacting, in an absorber column, an input gas stream containing CO2 with an aqueous absorption solution including NH3, MDEA, and potassium carbonate to generate a CCh-rich solution stream and a CO2- depleted gas stream. At 234, the method 230 includes generating, using a regenerator column, a CCh-lean solution stream and a CO2 gas stream from the CCh-rich solution stream.

[0103] In some embodiments, the method 230 further includes: (i) receiving, in a second absorber section of the absorber column or in a second absorber column with the aqueous absorption solution, a remaining portion of the input gas stream containing CO2 from the absorber column or a first absorber section of the absorber column; (ii) contacting the remaining portion of the input gas stream containing CO2 with theaqueous absorption solution to absorb CO2 and to generate a second CCh-rich solution stream; and (iii) generating, using the regenerator column, a second CCh-lean solution stream.

[0104] In some such embodiments, the method 230 further includes pumping: (i) the CCh-lean solution stream to the first absorber section of the absorber column or to the absorber column, (ii) the second CCh-lean solution stream to the second absorber section of the absorber column or to a second absorber column, wherein the second CCh-lean solution stream has a lower ratio of NFh / potassium carbonate than the first CCh-lean solution stream, and (iii) the CO2 depleted gas stream through a water wash to remove residual NH3 vapor. In some embodiments, the method 230 further includes passing CO2 gas stream through another water wash for purification, such for removing residual NH3 vapor before exiting the regenerator column.

[0105] In some embodiments, including any method and / or apparatus as described herein, the aqueous absorption solution(s) include about 0.1 mole (mol) to about 4 mol MDEA, about 0.1 mol to about 4 mol potassium carbonate, and about 1 mol to about 7 mol NH3. Embodiments are not so limited and can include sub-ranges within the disclosed ranges, such as about 1 mol to about 4 mol MDEA, about 1 mol to about 3 mol MDEA, about 1 mol to about 2 mol MDEA, about 0.5 mol to about 3 mol potassium carbonate, about 0.5 mol to about 2 mol potassium carbonate, about 0.5 mol to about 1 mol potassium carbonate, about 2 mol to about 7 mol NH3, about 3 mol to about 7 mol NH3, about 4 mol to about 7 mol NH3, about 5 mol to about 7 mol NH3, about 6 mol to about 7 mol NH3, and / or about 3 mol to about 6 mol NH3, among other ranges and combinations thereof.

[0106] In some embodiments, the method 230 can include contacting the input gas stream with the aqueous absorption solution while at a temperature between about 18 degrees C and about 45 degrees C, and generating the CCh-lean solution stream and the CO2 gas stream (e.g., a purified CO2 gas stream) while at a pressure between about 5 bar and about 20 bar and while at a temperature between about 30 degrees C and about 175 degrees C.

[0107] In some embodiments, the method 230 can include removing NH3 from the CCh-depleted gas stream using a water wash.

[0108] The method 230 can include additional variations, such as any of those described in connection with FIGs. 1A-1C and the operation of the apparatuses 100, 101, 103.

[0109] The various ranges provided herein include the stated range and any value or sub-range within the stated range. Furthermore, when “about” is utilized to describe a value, this includes, refers to, and / or encompasses variations (up to + / — 10%) from the stated value. Wt%, as used herein, includes or refers to a weight of a component as a percentage of the total weight of the composition or solution.

[0110] As used herein, the input gas stream or CO2 containing gas can include gas mixture. In embodiments, the input gas stream is a flue gas from a fossil fuel power plant or other such source. In embodiments, the input gas stream includes other components, such as one or more of N2, O2, NOx, SOx and other acid gases. In an embodiment the input gas stream is a flue gas including 5 to 15 vol % CO2, O2 with a balance N2 and small amounts of (less than 1%) NOx, SOx and other acid gases. In embodiments, the input gas stream includes CO2 in an amount between 2-20, or 2-15 vol %, or greater than 2, 3, 4, 5, 7, 10, or 15 vol %.

[0111] Reference throughout the specification to “examples”, “an example”, “embodiments” and so forth, means that a particular element (e.g., feature, structure, and / or characteristic) described in connection with the example is included in the example described, and may or may not be present in other examples. In addition, it is to be understood that the described elements for any embodiment may be combined in any suitable manner in various embodiments unless the context clearly dictates otherwise.

[0112] In describing and claiming the embodiments disclosed herein, the singular forms “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

[0113] Various embodiments are implemented in accordance with the underlying Provisional Application No. 63 / 592,513, filed October 23, 2023, and entitled “Advanced Mixed Salt Based Process for Removal of CO2 from Flue Gas Stream”, to which benefit is claimed and which is fully incorporated herein by reference in its entirety for its general and specific teachings. For instance, embodiments herein and / or in the Provisional Application can be combined in varying degrees (including wholly). Reference can also be made to the experimental teachings and underlying references provided in the underlying Provisional Application. Embodiments discussed in the Provisional Application are not intended, in any way, to be limiting to the overall technical disclosure, or to any part of the claimed disclosure unless specifically noted.EXPERIMENTAL EMBODIMENTS

[0114] Various experimental embodiments were conducted to generate and test different CO2 capture apparatuses. Such experiments including building benchapparatuses with absorber column(s) having an aqueous absorption solution that includes NH3, MDEA or a-MDEA, and potassium carbonate. Such apparatuses are sometimes herein referred to as “an advanced MSP (A-MSP) apparatus”, and the MSP solution containing MDEA or a-MDEA is sometimes referred at “an A-MSP solution”. Similarly, the apparatuses, whether including A-MSP or MSP may be referred herein as “a CO2 capture apparatus”.

[0115] Various experiments were directed to assessing aqueous absorption solutions and components thereof. In some embodiments, properties of components of the solutions were assessed, including diffusion coefficients of species and the NEE cycle.

[0116] FIGs. 3 A-3B illustrate diffusion coefficients of species and the NEE cycle at the gas-liquid boundary. In particular, the diffusion coefficients of FIG. 3 A are in water at 273 K. The presence of the NH3 cycle, shown in FIG. 3B, leads to increased nucleophilic [OFF] concentration in the system the promotes the CO2 absorption of MDEA. MDEA protonates rapidly in water (see Equation 8), and then the OH' reacts with CO2 to form bicarbonate similar to the CO2 absorption in K2CO3 (see Equation 9). The forward reaction in Equation 9 is slow without a promoter but is significantly enhanced in the presence of NH3.H2O + R1R2R3N OH' + R1R2R3N+(fast) Equation 8OH" + CO2 < — > HCO3' (slow without NH3) Equation 9

[0117] As further described below, FIG. 4A shows the rate enhancement is more than three-fold at about 15 kPA CO2 partial pressure (15% CO2) for an apparatus comprising two absorbers, e.g., absorber 1 and absorber 2.

[0118] FIGs. 4A-4B show the CO2 absorption rate and NH3 vapor pressure at absorber 2 under different conditions. In particular, FIG. 4A is a graph showing the enhancement of CO2 absorption rates in the presence of NH3 as a function of CO2 partial pressure at 40 degrees C. FIG. 4B is a graph showing NH3 vapor pressure at absorber under various CCh-loading conditions.

[0119] In embodiments that include two absorbers, absorber 1 (e.g., section 120-1 of FIGs. 1B-1C) has a high NH3 / (MDEA + K2CO3) ratio, and thus the CO2 capture is driven by the NH3. Absorber 2 (e.g., section 120-2 of FIGs. 1B-1C) is operated with lowNHs / (MDEA + K2CO3) ratio, and NH3 plays the role of an absorbent and a promoter, thus enhancing the slow absorptions reactions of MDEA and K2CO3. A significant capture rate enhancement in the second absorber is shown in FIG. 4A.

[0120] Low Ammonia Emission with Mixed Salts. During development, the dualabsorber apparatus was shown to be the most optimal way to operate an NEE-based absorption process at temperatures less than 20 degrees C with minimal NH3 slip. The regenerator column produced two lean streams with alkalinities of around 8M and around 4M (high and low NH3 / K for the two absorbers). The absorber 1 was operated with high NH3 / K (e.g., 3-4) and the absorber 2 was operated with low NH3 / K (less than 1) to maximize the absorption of CO2 from a CCh-containing gas stream and minimize NH3 carried over to the water wash with the scrubbed gas stream. The scrubbed gas stream (e.g., 107 of FIG. IB) from the water wash exit contained less than 10 ppm NH3, which met the emission requirements. FIG. 4B shows an example of the test results for 30 weight (wt)% MSP solution tested at 40 degrees C with the top sections of the absorber sections operating at 20 degrees C. The A-MSP solution behaved similarly to suppress the NH3 slip of the apparatus.

[0121] Effect of Temperature on the Rate of CO2 Absorption. The rate of CO2 absorption is increased by increasing the temperature of the solvent, with volatility being sufficiently low and the Gibbs free energy of the reaction being negative. At lower temperatures, the rates of reactions are low and the system equilibrium is slow. The absorbers were operated at a higher temperature (e.g., 20-45 degrees C) than conventional NFE-based processes (e.g., CAP at less than 5-10 degrees C) leading to fives time faster absorption kinetics.

[0122] FIG. 5 is a graph showing the gas transfer coefficient data obtained from a bench scale test of 30 wt% A-MSP solution indicating the effect of temperature on rate. In particular, FIG. 5 shows the observed rate of CO2 absorption into MSP solutions measured at varying CCh-lading at varying temperatures and at 1 bar. Similar to MSP, the A-MSP operates at a threshold absorption temperature range without any loss of solvent because MDEA is a high-boiling point liquid with low vapor pressure. From the equilibrium data, a 51 wt% A-MSP solution captured 90% or more CO2 from a flue gas stream (e.g., 15% CO2).

[0123] High-pressure CO 2 Regeneration and High Cyclic CO2Loading. Higher pressure regeneration and high CO2 loading capacity are key advantages to A-MSP.

[0124] FIG. 6 is a graph showing representative integrated test results. For example, the graph demonstrates 90% capture and regeneration of CO2 for 17-28 acfm simulated flue gas (15% CO2) stream (regenerator pressure: 11-15 bar; regenerator temperature: bottom-stage 155-160 degrees C, upper-stage 135-140 degrees C). CO2 loading capacities as high as 12.5 wt% (0.125 kg of CCh / kg solvent) with cyclic working capacity of 8.5 wt% (0.085 kg of CCh / kg solvent) were achieved. An A-MSP solution behaved similarly, providing a high loading capacity of CO2, but with the advantage of high-pressure CO2 regeneration at lower temperature (around 120 degrees C) as compared to prior MSP solutions, which significantly reduced reboiler energy demand.

[0125] Reduced Reboiler Heat Duty in Mixed-Salt Compositions. Regeneration of the solution is the main power consumer of the CO2 capture apparatuses. The required energy for solution regeneration comprises three terms: (i) AHsen- sensible heat for heating the solvent; (ii) AHvap - steam evaporation; and (iii) AHdes - the reaction heat. In MSP, AHsen is 70% lower than that of MEA-based technology because of the high CO2 loading. In addition, the regenerator operates at high pressure in the A-MSP with very low reflux ratio (H2O / CO2 less than 0.02), and thus AHvap is low. The processes that operate at lower pressures have high AHvap.

[0126] Reboiler duty for MSP at L / G 4.0 in an integrated apparatus was measured to be 2.2 megajoules (MJ) / kilogram (kg)-CO2. This can be reduced to below 2 MJ / kg-CCh with a lower L / G ratio (around 1) and high cyclic loading.

[0127] FIG. 7 is a graph showing a comparison of CO2 compositions in vapor phase for a CO2 rich mixed salt solution with MDEA added (51 wt% salt composition). More specifically, FIG. 7 shows the equilibrium data for the A-MSP solution containing NH3, K2CO3, and MDEA (up to 0.64 loading) at 90, 100, 110, and 120 degrees C. This data shows that the mixed salt with MDEA added (e.g., A-MSP) can generate even higher- pressure CO2 product at lower temperature than MSP.

[0128] FIG. 8 is a graph showing CO2 loading verses CO2 pressure at 100 degrees C for a 10 molal mixed salt and 10 molal MDEA-mixed salts. More specifically, FIG. 8 shows the equilibrium data comparing NH3, MSP, and A-MSP, which shows the high CO2 regeneration pressure advantage (e.g., about doubled for 0.55 loading) of A-MSP, e.g., MSP with MDEA added to the absorption solution. The A-MSP solution can release high-pressure CO2, at around 120 degrees C, significantly reducing the electrical power required for compressing CO2 to delivery pressures of greater than 2000 psi.

[0129] FIG. 9 is a graph showing power plant energy loss due to steam extraction, indicating that lower regeneration temperature and lower reboiler duty significantly improved net power output of the carbon capture integrated plant.

[0130] CCh Laboratory Test Data and Modeling

[0131] Absorption testing data from (small) bench-scale unit. An improved benchscale absorption apparatus to generate absorption isotherms was used. A parametric study was performed in which the compositions of the mixed salts and amine were varied while keeping the inlet gas at constant CCh to air ratio of 15 / 85 (vol% / vol%), More than twenty experiments spanning eleven different compositions were performed. For each experiment, the loading efficiency, pH, density, CCh partial pressure, and temperatures were recorded. The absorber column temperatures were kept at a constant 20 degrees C for the parametric study so that the data from all test runs could be compared equally, and to minimize NH3 loss. The reaction rate, CO2 partial pressure, pH, density and efficiency were measured and reported as a function of loading.

[0132] FIG. 10 is a graph showing efficiency as a function of CO2 loading for experiments at 20 degrees C. That is, FIG. 10. shows the efficiency of each solution as a function of CO2 loading. All compositions maintained a high level of efficiency (greater than 90%) and then experienced a gradual decline as the loading reached about 0.5; this is typical behavior for chemisorption reactions. The different compositions included varying amounts of MDEA, potassium carbonate, and NH3. For example, the concentration of MDEA was varied between 0.1 mol and 4 mol, the concentration of potassium carbonate was varied between 0.1 mol and 4 mol, and the concentration of NH3 was varied between 1 mol and 7 mol to form each of the compositions.Composition 522 maintained greater than 90% efficiency to a higher loading level than any other of the compositions.

[0133] FIGs. 11 A-l ID are graphs showing different groups of compositions and efficiency as a function of CO2 loading. In an attempt to elucidate the effects of each alkaline component, the runs were grouped as shown in FIGs. 11 A-l ID as: (a) 52X, (b) X22, (c) 5X2, and (d) other, where “X” was the varying component and the other two components were held constant. In particular, the group in FIG. 11 A has varied MDEA, with NH3 and potassium carbonate held constant. The group in FIG. 1 IB has varied NH3, with MDEA and potassium carbonate held constant. The group in FIG. 11C has varied potassium carbonate, with MDEA and NH3 held constant. FIG. 1 ID shows runs that did not fit into the pattern of the groups of FIGs. 11 A-l 1C. FIG. 11 A showsincreasing the MDEA reduced the efficiency for a given load except for Composition 522, which had the highest efficiency per loading. FIG. 1 IB shows increasing NH3 increased efficiency, again except for Composition 522. FIG. 11C and FIG. 1 ID show that Composition 522 had the highest efficiency for a given loading. Because of the lack of distinct pattern emerging from the graphs of FIGs. 11 A-l 1C, different runs were repeated to assess whether the results were repeatable. The increased efficiency is likely due to a synergistic effect caused by the addition of MDEA. Previous studies have shown that when different carbon capture solutions are combined (called “promoted solutions”), the resulting promoted mixture can have significantly improved performance compared to the individual solutions. This includes NFE-potassium carbonate performed in the lab, including mixing potassium carbonate with various ammines, mixing NH3 with amines, and a plethora of other examples. The Composition 522 is an example of a promoted solution that outperforms its individual components.

[0134] FIGs. 12A-12B are graphs showing the effect of temperature on efficiency and absorption rate at varying the CO2 loading for Composition 522. General trends show that increasing the loading decreased both efficiency and absorption rate, and a maximum was reach between 15 degrees C and 22 degrees C. As the temperature deviated from this maximum in either direction, the effect of loading became more pronounced. At the elevated temperatures and higher loading, the reverse reactions became more pronounced and more CO2 was desorbed than at lower temperatures, leading to the lower efficiency and absorption rates. FIG. 12A shows the effects of temperature on efficiency and FIG. 12B shows the effects of temperature on absorption rate for a given loading.

[0135] FIGs. 13A-13B show modeling and laboratory measurements of CO2 partial pressure variations with CO2 loading for the Composition 522 at two temperatures. The measured data agreed with the predicted values from the model, suggesting that the model can be used for complete flowsheet modeling. In particular, FIG. 13A-13B show a comparison of the calculated CO2 vapor pressure data variation with CO2 loading with measured values at 22.5 degrees C (FIG. 13A) and 30 degrees C (FIG. 13B) for Composition 522.

[0136] Regeneration testing data from (small) bench-scale unit. The static autoclave was used to test CO2 desorption as the function of temperature for the solution compositions that were tested. The goal was to achieve a CO2 pressure of greater than 10 bar at a temperature lower than 120 degrees C. The CCh-rich solutions (e.g., CO2loaded streams) after absorption experiments were run, were regenerated in a static autoclave setup. The autoclave was filled with 300 milliliters (mL) of CCh-rich solutions, and most solutions had a starting CO2 loading of greater than 0.5. The apparatus was first purged and pressurized with nitrogen (N2) to remove air and check for leaks. The apparatus was vented to bring the pressure down to ambient, and then the apparatus was rapidly heated to greater than 140 degrees C and was allowed to equilibrate and then slowly cooled. During the cool down, the temperature and pressure data was collected via a computer program. The resulting equilibrium vapor pressure curves are shown in FIG. 14. All runs tested showed the potential to meet the goal of greater than 10 bar CO2 pressure at temperatures of less than 120 degrees C.

[0137] FIG. 14 is a graph showing the desorption curves using a static autoclave setup.

[0138] Testing in a (large) Bench-Scale Integrated Apparatus

[0139] Integrated Apparatus . FIG. 15 shows a schematic of an absorber block including two absorber columns with a water wash column (e.g., humidifier) added to the front end of the absorber columns for saturating the incoming gas (e.g., flue gas) with water. Water for the front water wash column was fed from the scrubbed gas water wash column bleed and so overall water consumption of the apparatus was not impacted. This front water wash column represents a direct contact cooler (DCC) in the integrated CO2 capture apparatus. Input gas and the DCC / water wash column was downstream (e.g., on the left side) of the mass flow controllers. In the absorber block, two mass flow controllers, one for air and one for CO2, were used to make the desired composition of synthetic gas. The gas was passed through the DCC, absorber, absorber 2, and the water wash. The CO2 and NH3 concentrations were measured at the inlet of the DCC and the outlet of each column.

[0140] FIG. 16 shows a schematic of a regenerator column. The process of operation of the regenerator was as follows. The CCh-rich solution (e.g., rich liquid 1) from absorber 1 is split to about 80:20 and pumped into the regenerator column at two stages as shown, with about 20% going to the upper stage and the balance going to the middle stage. The CCh-rich solution (e.g., rich liquid 2) from absorber 2, which has a lower NH3 concentration than the CCh-rich solution (e.g., rich liquid 1) from absorber 1, is pumped to the upper stage of the regenerator column. The CCh-rich solution, which is liquid, is cooled to 15 degrees C to reduce NH3 emissions from the regenerator column. As a polishing step, a high-pressure water wash is mounted at the top (e.g., near the CO2 output) of the regenerator column such that the exiting CO2 gas has less than 10 ppmNH3content. The regenerator energy for the reboiler was provided by steam (175 degrees C). The vapor stream from the reboiler was passed through the bubble caps and the liquid hold in the regenerator column. The temperature of this solution (e.g., rich liquid 1) can be varied up to 140 degrees C, and the CCh-lean solution (lean liquid 1) for absorber 1 is drawn from the lower middle stage of the regenerator column. The CO2- lean solution (lean liquid 2) for absorber 2 was drawn from the bottom stage of the regenerator column, and the temperature of the bottom stage can be varied up to 160 degrees C. The regenerator column was operated under isobaric conditions with a temperature gradient of around 40-60 degrees C at the top stage and around 160 degrees C at the bottom stage. There were temperature sensors along the regenerator column to record temperature profiles of the apparatus. Two main heat exchangers recover the sensible heat from the regenerated solution to heat the incoming CCh-rich solution streams. The flowsheet model of the process indicated that the outgoing CCh-lean solution streams from the heat exchangers were around 40 degrees C and needed to be cooled to between about 15 degrees C and about 20 degrees C before being fed to the absorber columns. As such, two cooling coils were installed on the CCh-lean solution return paths (e.g., conduits).

[0141] For continuous operator of the regenerator column, the input C Ch-rich solution streams and output CCh-lean solution streams to and from the regenerator were balanced, and the liquid level draws of the regenerator stages were controlled. There were flow meters and level sensors that were actively monitored by the controller, which controls pumps, valves, and steam flow to maintain the pressure, temperature, and flow rates of the operator-specific parameters.

[0142] Parametric and Steady State Testing in the (large) Integrated Bench-Scale Apparatus. Synthetic flue gas was generated by mixing dry building compressed air and carbon dioxide from liquified gas tanks. The input gas stream was saturated with water at the input temperature representing a flue gas stream from a power plant. The aqueous absorption solution, e.g., A-MSP solution, was designed with higher molality and reduced water content. The vapor conduits and the CO2 back pressure control value in the regenerator column were heat traced at a higher temperature to avoid solid condensation.

[0143] During parametric testing, the CO2 feed concentration was held constant (around 15%) while the reboiler and middle stage of the regenerator temperature, regenerator pressure, absorbent solvent recycle rate, total gas flow rate, alkalinemolarity, and recycle rate between the regenerator and absorber columns were changed as listed below in Table 1. In steady state runs, apparatus parameters were held constant for the entire duration of the test.Table 1 : Parametric Test Matrix

[0144] The data for the analysis was collected when the apparatus was in steady condition. After changing parameters, the apparatus took some time to reach a steady condition. Once the steady state was reached, there was no fluctuation in flows, concentrations, and dynamics of the apparatus. The criteria applied to identify the steady condition was when no change in the CO2 concentration of the exit gases from absorber 1 and absorber 2 was observed. Then, a time interval of around ten minutes was selected to get an average from all data in the time interval.

[0145] Table 2 is a representative sample of the integrated experiments. The CO2 absorption efficiency was calculated based on the gas side (e.g., CO2 composition in the input and the output) and the liquid side (e.g., CO2 loading in the rich liquid solution streams). A greater than 95% mass balance was achieved from the comparison.Therefore, the gas side measurements were used for determining the CO2 capture efficiency. As shown in Table 2, more than 90% CO2 capture efficiency was obtained.Table 2: Representative Sampling of Data*CO2capture efficiency was calculated based on CO2 concentration of absorber 2 output gas.

[0146] Runs 86 to 88, 90 to 94, and 95 to 97 had the same process condition as the run with the A-MSP apparatus in steady condition for more than six hours.

[0147] FIG. 17 is a graph showing the stability of the temperature of lean liquid 1 and lean liquid 2 drawn from the bottom and top regenerator stages during a six hour long run. The apparatus reached steady state about thirty minutes after a parameters change. As it is the characteristic of the steady state condition, the pressure and temperature remain constant during the run of the apparatus. However, the CO2 flow fluctuates because the CO2 pneumatic control valve opens and closes rapidly to adjust the pressure inside the regenerator column as shown by FIG. 18.

[0148] FIG. 18 is a graph showing regenerator pressure and CO2 flow rate during a six hour long run. Rapid CO2 flow fluctuation did not affect the dynamics of the regeneratorcolumn, and pressures and temperatures remained constant during the run. The CO2 flow fluctuations can be minimized with proper valve control parameters: proportional band, integral time, and derivative time. The average CO2 flow values were obtained by a curve fit as shown in FIG. 18, which also shows the steady conditions during the six hour run.

[0149] Next-Generation Modeling for Technoeconomic Analysis (TEA)

[0150] Flowsheet modeling. The process flowsheet model was developed using OLI Systems™ flowsheet modeling program. The addition of MDEA to the solvent necessitated an updated to the databank in the OLI software to incorporate the interactions of MDEA with CO2 and the other components of the solvent. The thermodynamic data for the amine and the mixed salt components were measured and the OLI database was updated with the measured parameters. Prior to the update, several simulations were performed and the results did not agree well with the experimental data, namely for the regenerator temperature and heat of absorption. After OLI performed a databank update to incorporate newer, higher-quality vapor-liquid equilibrium (VLE) data, the stimulation results agreed with the experimental results.

[0151] FIGs. 19A-19B show flowsheet models for A-MSP apparatuses. FIG. 19A shows a flowsheet model for a complete A-MSP apparatus. This flowsheet was used to model the apparatus at a scale of a 550 megawatt electric (Mwe) plant. Heat and mass balances of streams were scaled and generated for the TEA. The flowsheet model was optimized with heat integration and obtained a complete stream table with mass and heat balances data. FIG. 19B is another flowsheet model for a complete A-MSP apparatus that includes a single absorber column, no flash stripper, and a single CCh-lean stream.

[0152] Process Simplification. Once the flow sheet modeling was validated with measured data, several process modifications in the flowsheet model were performed and compared to the stream data. The objective was to reduce the process components and determining the impact on the capture efficiency and energy demand. Two main simulations, summarized in Table 3, were performed using the updated databank. The first stimulation used a process confirmation including two absorbers, and two streams with different compositions as shown in FIG. 19A. This stimulation also incorporated a splash column where a fraction of incoming flue gas contacts the lean liquid 2 stream to remove some NH3 from the stream prior to sending to the absorber 2. A splash column is similar to a water wash, but smaller in size, with liquid being splashed to strip some volatiles. The second simulation used a simplified configuration with only one absorber,no splash column, and a single lean liquid stream, as shown in FIG. 19B. All cases modeled to obtain 90% CO2 capture rate. The reboiler duty, regeneration temperature, and emissions were compared for the two cases.Table 3: Simulated Cases at TEA Scale with Updated MDEA databank

[0153] Table 4 summarizes the results of the two simulated cases. The energy consumptions (total reboiler duty) values were similar between the two cases. Because of the elimination of one absorber and the splash column, the CAPEX is expected to be significantly lower in the second case.Table 4: Summary of Results

[0154] Corrosion Studies

[0155] Corrosion measurements for 304SS, 316SS, and carbon steel were performed simulating absorber conditions. 304SS and 316SS corrosion test were performed for regenerator conditions. The test were performed in autoclaves with A-MSP solutions with different CO2 loading over four weeks of exposure. The corrosion rates of metals in the A-MSP solutions were lower than that of MEA as shown by FIG. 20. Based on this, the absorber(s) of the A-MSP apparatus can be designed with carbon steel at a significantly reduced cost. Table 5 summarizes the results.Table 5: Corrosion of 304SS, 316SS, and carbon steel

[0156] FIG. 20 is a graph of corrosion rates of 304SS and 316SS when immersed in loaded and unloaded MEA solutions at 25, 40, and 80 degrees C.

[0157] Although specific embodiments have been illustrated and described herein, a variety of alternate and / or equivalent implementations can be substituted for the specific embodiments shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein.

Claims

CLAIMS1. An apparatus comprising: an absorber column including an aqueous absorption solution and configured to contact an input gas stream containing carbon dioxide (CO2) with the aqueous absorption solution which absorbs CO2 from the input gas stream to generate a CCh-rich solution stream, the aqueous absorption solution including ammonia (NH3), methyl diethanol amine (MDEA), and potassium carbonate; and a regenerator column configured to receive the CCh-rich solution stream and output a CCh-lean solution stream and a CO2 gas stream.

2. The apparatus of claim 1, wherein the regenerator column is configured to regenerate the aqueous absorption solution as the CCh-lean solution stream at a temperature of between about 100 degrees Celsius (C) and about 175 degrees C, or about 120 degrees C.

3. The apparatus of claim 1, wherein the regenerator column is configured to generate the CCh-lean solution stream and the CO2 gas stream from the CCh-rich solution stream at a pressure of between about 5 bar and about 20 bar and with a temperature gradient of about 30 degrees Celsius (C) to about 175 degrees C.

4. The apparatus of claim 1, wherein the aqueous absorption solution captures between 90 percent and 100 percent of the CO2 from the input gas stream and generates a CCh-depleted gas stream.

5. The apparatus of claim 1, further including a heat exchanger coupled to the absorber column and configured to transfer heat between the heat exchanger and the input gas stream such that the input gas stream is at a temperature between about 18 degrees Celsius (C) to about 45 degrees C while input or prior to being input to the absorber column.

6. The apparatus of claim 1, further including: a second absorber column including the aqueous absorption solution and configured to contact a remaining portion of the input gas stream containing CO2 with the aqueous absorption solution and to generate a second CCh-rich solution stream, and wherein the regenerator column is further configured to receive the second CCh- rich solution stream and output a second CCh-lean solution stream.

7. The apparatus of claim 6, further including pumps and valves configured to provide the CCh-lean solution stream to the absorber column and the second CCh-lean solution stream to the second absorber column, the CCh-lean solution stream having a higher ratio of Nfh / potassium carbonate than the second CCh-lean solution stream.

8. The apparatus of claim 1, wherein: the absorber column includes first and second absorber regions with the aqueous absorption solution; the first absorber region is configured to contact the input gas stream containing CO2 with the aqueous absorption solution, generate the CCh-rich solution stream, and provide a remaining portion of the gas stream containing CO2 to the second absorber region; the second absorber region is configured to contact the remaining portion of the input gas stream containing CO2 with the aqueous absorption solution and generate a second CCh-rich solution stream from the remaining portion of the input gas stream containing CO2; and the regenerator column is configured to receive the CCh-rich solution stream and the second CCh-rich solution stream and to output the CCh-lean solution stream, a second CCh-lean solution stream, and the CO2 gas stream.

9. The apparatus of claim 1, further including a water wash coupled to the regenerator column and configured to capture NH3 from the CO2 gas stream exiting from the regenerator column.

10. The apparatus of claim 1, further including a water wash coupled to the absorber column and configured to capture NH3 from the input gas stream with CO2 removed.

11. The apparatus of claim 1, wherein the MDEA includes activated-MDEA (a- MDEA).

12. An apparatus comprising: a first absorber section and a second absorber section in an absorber column, each of the first and second absorber sections including an aqueous absorption solution containing ammonia (NH3), methyl diethanol amine (MDEA), and potassium carbonate, wherein: the first absorber section is configured to contact an input gas stream containing carbon dioxide (CO2) with the aqueous absorption solution which absorbs CO2 from the input gas stream to generate a first CCh-rich solution stream; and the second absorber section is configured to contact a remaining portion of the input gas stream containing CO2, as received from the first absorber section, with the aqueous absorption solution which absorbs CO2 from the remaining portion of the input gas stream to generate a second CCh-rich solution stream and a CCh-depleted gas stream; and a regenerator column configured to receive the first and second CCh-rich solution streams and output a first CCh-lean solution stream to the first absorber section, a second CCh-lean solution stream to the second absorber section, and a CO2 gas stream.

13. The apparatus of claim 12, wherein the aqueous absorption solutions are in packed sections of the first and second absorber sections which operate at between about 18 degrees Celsius (C) and about 45 degrees C.

14. The apparatus of claim 12, wherein the regenerator column is configured to generate the CO2 gas stream from the first and second CCh-rich solution streams at a pressure of between about 5 bar and about 20 bar and with a temperature gradient of about 30 degrees Celsius (C) to about 175 degrees C.

15. The apparatus of claim 12, wherein the absorber column includes a first absorber column containing the first absorber section and a second absorber column containing the second absorber section.

16. The apparatus of claim 12, wherein the first absorber section is positioned vertically adjacent to the second absorber section in the absorber column.

17. A method comprising: contacting, in an absorber column, an input gas stream containing carbon dioxide (CO2) with an aqueous absorption solution including ammonia (NH3), methyl diethanol amine (MDEA), and potassium carbonate to generate a CCh-rich solution stream and a CCh-depleted gas stream; and generating, using a regenerator column, a CCh-lean solution stream and a CO2 gas stream from the CCh-rich solution stream.

18. The method of claim 17, further including: receiving, in a second absorber section of the absorber column or in a second absorber column with the aqueous absorption solution, a remaining portion of the input gas stream containing CO2 from the absorber column or a first absorber section of the absorber column; contacting the remaining portion of the input gas stream containing CO2 with the aqueous absorption solution to absorb CO2 and to generate a second CCh-rich solution stream; and generating, using the regenerator column, a second CCh-lean solution stream.

19. The method of claim 18, further including pumping: the CCh-lean solution stream to the first absorber section of the absorber column or to the absorber column; the second CCh-lean solution stream to the second absorber section of the absorber column or to a second absorber column, wherein the second CCh-lean solution stream has a lower ratio of Nfh / potassium carbonate than the CCh-lean solution stream; andthe CO2 depleted gas stream through a water wash to remove residual NH3 vapor.

20. The method of claim 17, wherein the aqueous absorption solution includes: about 0.1 mole (mol) to about 4 mol MDEA; about 0.1 mol to about 4 mol potassium carbonate; and about 1 mol to about 7 mol NH3.

21. The method of claim 17, wherein: contacting the input gas stream with the aqueous absorption solution while at a temperature between about 18 degrees Celsius (C) and about 45 degrees C; and generating the CCh-lean solution stream and the CO2 gas stream while at a pressure between about 5 bar and about 20 bar and while at a temperature between about 30 degrees C and about 175 degrees C.

22. The method of claim 17, further including removing NH3 from the CCh-depleted gas stream using a water wash.

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